Nippon Telegraph and Telephone Corporation

Hiroyuki Ohtsuka

Tadashi Shirato

Hideaki Matsue

Takehiro Murase

In a digital demodulation system (FIGS. 2, 3, 4, 7, 8) in a dual polarization radio system, having a first demodulator (4) and a first A/D converter (14) for a main signal, a second demodulator (5) and a second A/D converter (15c) for an interference signal (cross polarization signal), a transversal filter (18) for providing a compensation signal for cancelling an interference component in the main signal depending upon the demodulated interference component; the second A/D converter (15c) for providing the interference component in digital form is operated with a clock signal (102) regenerated in the main signal branch (4, 14) so that system operates correctly even when the main signal and cross polarization signal are in an asynchronous condition. The A/D converter (14, 15c, 105) is provided with an attenuator (104) for compressing amplitude of an input signal to avoid saturation of the circuit (105) in case of fading and/or distortion, and a ROM table (107) for correcting digitalized output after equalization and/or cancellation. Tap coefficients of the transversal filter (18) are obtained by a control (19) through a ZF method when inter-symbol interference is small, and a MLE method when inter-symbol interference is large. Further, an integration constant for the coefficients is adaptive depending upon inter-symbol interference.

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Kanagawa, Japan

Hiroyuki Ohtsuka